1. Field of the Invention
The present invention relates to a light curing composition for dental restoration and, more particularly, to a light curing composition for dental restoration which shows high sensitivity with respect to light sources for emitting both visible light and ultraviolet light, and provides a polymerization-cured mass excelling in color stability and physical properties.
2. State of the Prior Art
As well known in the art, the so-called chemical curing type and light curing type of dental composite resins for restoration are used in dentistry to which the invention belongs. The chemical curing type of composite resins for filling is a pasty product composed mainly of a finely divided inorganic filler and a binder resin for bonding together filler particles. This pasty product is divided into two portions, one portion containing a peroxide and the other portion containing an amine. For use, these pasty portions are mixed together, and the resulting mixture is filled in a dental caries cavity. Thereafter, the binder-resin are polymerized and cured by the peroxide-amine redox reaction within a certain period of time. In view of manipulation, this type of resin has a disadvantage that its curing time is so certain that an operator should finish filling work while the paste still maintains its plasticity prior to curing.
With reference to the light curing type of composite resins for filling which makes use of a photo-polymerization catalyst in place of the peroxide-amine base catalyst used for chemical polymerization, the curing reaction does not proceed, unless they are exposed to light. For that reason, they have a number of advantages that their mainipulation and curing time is substantially controlled depending upon an operator's will so as to obtain the optimum results in respect of the treatment procedure and time to be applied. In dentistry, the light curing type of filling materials now enjoys increasing use.
Out of a number of compositions for the light curing type dental filling materials known in the art, there are often used visible light curing type of filling materials in view of the fact that they can securely be used in the oral mouth, in particular. For instance, such compositions are disclosed in British Pat. No. 1,408,265 as well as Japanese Patent Laid-Open Publication Nos. 57-187377, 53-62394, 57-54107, 57-77609 and 58-65704, which relate to the use of an alpha-diketone and a reducing agent, as disclosed in British Pat. No. 1,408,265 specification. In most cases, however, actually available products make use of camphor quinone.amine combinations.
The visible light curing type of filling materials cures in a wavelength region of 400-500 nm, but does not provide any satisfactory cured mass in a wavelength region of below 400 nm. They are also susceptible to the intensity of light, so that insufficient reactions tend to take place in a portion away from a light-emitting source, leaving a larger amount of the residual monomer behind. This often results in deteriorations in the color stability and physical properties from the clinical point-of-view.
Ultraviolet light curing type of dental compositions is known from Japanese Patent Publication No. 51-2235 and Japanese Patent Laid-Open Publication No. 53-82088, for instance. Ultraviolet light having a wavelength of 300 nm or lower cannot directly be used in the oral mouth, since they are harmful to the human body. As pointed our previously, their defect is a limited curing depth.
The aforesaid two types of filling compositions are designed to cure in their exclusive wavelength regions. Thus, any light curing type of polymerizable compositions is not still known in the art, which are capable of curing well in both ultraviolet and visible light regions.